Keynote for Mac mini

Keynote is downloaded from the App Store, an application found in the Applications folder.

If you have installed Keynote before, you can do so again, sign in to the App Store and search for Keynote, if you haven't downloaded it previously, only the latest version will be available which requires Mac OS Catalina.

As stated previously, Keynote for High Sierra is not available to unless you have downloaded Keynote previously.

If Keynote is your prime interest, find out if you can update to Catalina which will then allow you to download the latest version of Keynote, look at this Apple page for hardware requirements for Catalina:

Mac OS Catalina is compatible with these computers

As at May 2010,

• the latest version of Keynote, (version 10.0) is not compatible with Sierra OS 10.12, or High Sierra 10.13 or earlier Mac OS versions, therefor the App Store will not allow version 10.0 to be downloaded.
• the latest version of Keynote can only be downloaded if running either Mac OS Mojave or Catalina as those are the only Mac OS that can run the latest version of Keynote
• an older version of Keynote can be downloaded, if you have previously downloaded that version.
• if you have not downloaded any version of Keynote before, only the latest version is available

As to alternatives, there are plenty third party slide show applications available, including these freeware applications from; Libra Office, Free Office and Open Office.

If your MacMini is a late 2012, you can install Catalina then install Keynote version 10. I have a 2012 MacMini here dedicated to graphics work and is working perfectly with Catalina. Be aware Catalina is 64 bit only, any older 32 bit applications will not instal - things like some printer drivers, old version of MS Office and older Adobe products.

If you are without any presentation application, at least download and install the very latest version of Libra Office it is 100% reliable and 100% free from here: Libra Office Download